Ten Multi-planet Systems from K2 Campaigns 1 & 2 and the Masses of Two Hot Super-Earths
Sinukoff et al
We present a catalog of 10 multi-planet systems from Campaigns 1 and 2 of the K2 mission. We report the sizes and orbits of 24 planets split between six 2-planet systems and four 3-planet systems. These planets stem from a systematic search of the K2 photometry for all dwarf stars observed by K2 in these fields. We precisely characterized the host stars with adaptive optics imaging and analysis of high-resolution optical spectra from Keck/HIRES and medium-resolution spectra from IRTF/SpeX. The planets are mostly smaller than Neptune (19/24 planets) as in the Kepler mission and all have short periods (P less than 50 d) due to the duration of the K2 photometry. The host stars are relatively bright (most have Kp less than 12.5 mag) and are amenable to follow-up planet characterization. For EPIC 204221263, we measured precise radial velocities using Keck/HIRES and provide initial estimates of the planet masses. EPIC 204221263b is a short-period super-Earth with a radius of 1.55±0.16 R⊕, a mass of 12.0±2.9 M⊕, and a high density consistent with an iron-rich composition. The outer planet EPIC 204221263c is a lower density sub-Neptune-size planet with a radius of 2.42±0.29 R⊕ and a mass of 9.9±4.6 M⊕ that likely has a substantial envelope. This new planet sample demonstrates the capability of K2 to discover numerous planetary systems around bright stars.